1. Field of the Invention
The presently disclosed and/or claimed inventive process(es), procedure(s), method(s), product(s), result(s), and/or concept(s) (collectively referred to hereinafter as the “presently disclosed and/or claimed inventive concept(s)”) relates generally to a slurry for use in battery electrodes and methods of preparing such. More particularly, but not by way of limitation, the presently disclosed and/or claimed inventive concept(s) relates to the slurry comprising a binder composition comprising a modified guaran. Additionally, the presently disclosed and/or claimed inventive concept(s) relates to compositions of electrodes and methods of making the electrodes, either anodes and/or cathodes, with the binder composition comprising the modified guaran.
2. Background of the Invention
Lithium batteries are used in many products including medical devices, electric cars, airplanes, and most notably, consumer products such as laptop computers, cell phones, and cameras. Due to their high energy densities, high operating voltages, and low-self discharges, lithium ion batteries have overtaken the secondary battery market and continue to find new uses in products and developing industries.
Generally, lithium ion batteries (LIBs) comprise an anode, a cathode, and an electrolyte material such as an organic solvent containing a lithium salt. More specifically, the anode and cathode (collectively, “electrodes”) are formed by mixing either an anode active material or a cathode active material with a binder and a solvent to form a paste or slurry which is then coated and dried on a current collector made of a material, such as aluminum or copper, to form a film on the current collector. The anodes and cathodes are then layered or coiled prior to being housed in a pressurized casing containing an electrolyte material, which all together forms a lithium ion battery.
When making electrodes, it is important to select a binder with sufficient adhesive and chemical properties such that the film coated on the current collector will maintain contact with the current collector even when manipulated to fit into the pressurized battery casing. Since the film contains the electrode active material, there will likely be significant interference with the electrochemical properties of the battery if the film does not maintain sufficient contact with the current collector. Additionally, it is important to select a binder that is mechanically compatible with the electrode active material(s) such that it is capable of withstanding the degree of expansion and contraction of the electrode active material(s) during charging and discharging of the battery. As electrode active materials continue to evolve, binders will need to continue to adapt in order to remain mechanically compatible with the evolving electrode active materials. If not, large capacity fades during cycling can result from the use of new electrode active materials like, for example, silicon-containing with currently existing binder compositions. As such, binders play an important role in the performance of lithium ion batteries.
Currently, lithium ion battery technology generally teaches binder compositions comprising cellulosic materials selected from carboxymethylcellulose, carboxyethylcellulose, aminoethylcellulose, and/or oxyethylcellulose. More specifically, carboxymethylcellulose (CMC) has become the preferred choice of cellulose material to be included in LIB binders comprising graphite as the anode active material. See, for example, US 2004/0258991 filed by Young-Min Choi et al., hereby incorporated herein by reference in its entirety. Binder compositions comprising these cellulose derivatives alone may not have the mechanical properties necessary, however, to support the large volume changes that occur with some of the electrode active materials currently interested.
Specifically, silicon-containing material has recently come to the forefront as a promising anode active material for LIBs. See, for example, B. Lestriez et al., On the Binding Mechanism of CMC in Si Negative Electrodes for Li-Ion Batteries, Electrochemistry Communications, vol. 9, 2801-2806 (2007), which is hereby incorporated herein by reference in its entirety. Some of the reasons that silicon-containing material has come to the forefront as a promising anode active material are: its high theoretical specific capacity of 4200 mAhg−1 for Li4.4Si, low electrochemical potential between 0 and 0.4 V versus Li/Li+, and a small initial irreversible capacity compared with other metal- or alloy-based anode materials. See, B. Koo et al., A Highly Cross-linked Polymeric Binder for High-Performance Silicon Negative Electrodes in Lithium Ion Batteries, Angew. Chem. Int. Ed. 2012, 51, 8762-8767, hereby incorporated herein by reference in its entirety. It has been found herein that a specific capacity of about 600 mAhg−1 can be achieved by mixing graphite with silicon oxide (SiOX) and conductive carbon at a weight ratio of about 0.795/0.163/0.042 and, alternatively, a specific capacity of about 450 mAhg−1 can be achieved by mixing graphite with silicon oxide at a weight ratio of about 92 to 5, both of which increase the specific capacity of the anode material above the 340 mAhg−1 associated with graphite independent of any other electrode active material. Silicon-containing material has been known, however, to undergo large volume changes during charging and discharging, which can cause problems for a battery's capacity and overall performance.
The presently disclosed and/or claimed binder compositions comprising a guaran and/or modified guaran, however, actually improve the capacity of lithium ion batteries comprising a silicon-containing electrode active material. This is due in part to guaran having a high molecular weight and strong adhesive properties, which contribute to guaran being capable of withstanding the large volume changes generally associated with silicon-containing electrode active materials.